THURSDAY, Nov. 19, 2015 (HealthDay News) -- Childhood cancer survivors can have poor mental and physical health as adults, according to two new studies.

These health problems may be related to some of the toxic medications needed to treat cancer, experts say.

"We are doing a lot better at curing childhood cancers, but there are a lot of late effects of treatment that need to be looked at," said Dr. Karen Effinger, a pediatrics instructor at Stanford School of Medicine. Because they are so young when treated, children and teens with cancer are the most vulnerable to long-term effects of treatment, she noted.

In one study, Danish researchers found that cancer survivors were more likely to be hospitalized as adults. In the other, kids who survived bone cancer were more likely to have poor reading and thinking skills, investigators found.

Both studies were published Nov. 19 online in JAMA Oncology.

"Survivors after cancer in adolescence and young adulthood should be knowledgeable about their increased risk for health problems related to their treatment," said Kathrine Rugbjerg, of the Danish Cancer Society Research Center in Copenhagen.

"Increased attention to symptoms that might indicate a disease and being treated early might prevent a disease from developing," added Rugbjerg. She led a study of the hospitalization risk for more than 33,000 young cancer survivors who were diagnosed from 1943 through 2004.

Survivors of leukemia, brain cancer or Hodgkin lymphoma had the highest risk of hospitalization -- roughly double -- up to 34 years after their battle with cancer, the study found.

Overall, the researchers identified more than 53,000 hospitalizations for at least one of 97 diseases, including cancer; heart, lung or endocrine diseases; nervous system disorders, and infectious diseases, she said.

In the other and smaller study, lead researcher Kevin Krull, of St. Jude Children's Research Hospital in Memphis, and colleagues examined the mental abilities of survivors of childhood osteosarcoma, a type of bone cancer.

These cancer survivors had lower scores in reading, attention, memory and the speed at which their brain processes information, Krull said.

But a powerful drug used to treat osteosarcoma -- methotrexate -- doesn't seem to have caused that mental decline, the study concluded.

The study included 80 patients with an average age of nearly 39, whose cancer was diagnosed almost 25 years earlier. The researchers compared them with 39 people who had not had cancer.

Krull said that although methotrexate is linked to brain problems when given in high doses, the survivors' mental impairment appeared related to current health conditions, not that drug.

But these patients also reported having heart problems, he said. "These problems could result from another type of drug these patients received, called anthracyclines, which can damage the heart, Krull said.

"These heart problems are producing reduced blood flow to the brain," he said. "These heart difficulties seem to be causing the mental problems."

Whatever the cause, the mental problems have real-world consequences, Krull said. Survivors with mental problems were less likely to graduate college. They were also almost four times more likely to be unemployed and three times more likely to earn less than $40,000 a year, he said.

"Care of the cancer patient doesn't stop with the cancer," Krull said. "We have to continue to monitor these chronic health conditions because they can impact brain growth and development and affect daily life skills."

Effinger, who co-authored of an accompanying editorial in the journal, called for more study on the long-term consequences of cancer treatment in kids.

"We know that there are late effects that come from treatment, and we need to figure out what we can do to reverse those effects and protect patients and give them an improved quality of life," she said.